Provided is a strand extending in the longitudinal direction, wherein the strand includes filaments of one type having a gradient-length effect through spiral rotational twists and an irregular fine texture through self-thermal shrinking. The filaments of the strand have natural coiling characteristics that are very similar to those of natural hair of black people, and these characteristics are caused by the facts that the filaments have 3-dimensional waveforms occurred due to many fine and irregular windings or projections and that the waveforms exhibit fractal structure features and a fine kinky texture.